A MULTIPURPOSE FIRMNESS TESTER FOR FRUITS AND VEGETABLES

A computer driven testing system has been developed to measure the firmness and other physical properties of fruit and vegetables rapidly and easily. The system has multiple functions and can be used for a range of crops in either destructive or non-destructive mode. Measurements made include skin firmness or rupture strength, flesh firmness at any given depth, compressibility, modulus of elasticity, energy absorption during a loading cycle, and compression strength between flat plattens. The system has the ability to instantaneously record both load and displacement, and then feed this information into the indenter movement control to make immediate alterations to the indenter movement. The system consisted of a computer with a multi-function input/output (I/O) card and two computer controlled stepper motors which drove a vertical column at up to 4 mm s(-1). Various indenters could be attached to the column to compress or crush the fruit sample. The specimen to be sampled was placed on a load cell under the indenter column, and the output from the load cell was fed to the computer at a sampling rate of 40 kHz through an analogue/digital (A/D) converter. The computer was programmed to conduct the required test measurements as soon as the specimen was detected. In this way measurements could be taken by inexperienced personnel. Each test took under 30 s to complete, and results were fed back to the user immediately. Examples of measurements on tomatoes, apples and cherries are presented to demonstrate the type of output data obtained.